1. Field of the Invention
The present invention generally relates to computer systems, and more particularly to a method of cooling components in a data storage device have moving parts which generate air flow, such as a hard disk drive having one or more spinning disks.
2. Description of the Related Art
Computer systems use a variety of devices for permanently storing data, i.e., in a non-volatile manner such that power to the computer system may be turned off but the data (including both user information and computer programs) are retained for future access. These storage devices typically use a magnetic or optical medium to preserve the data. The most common data storage device has one or more generally circular disks formed from a non-magnetic substrate with a ferromagnetic coating. The disks rotate or spin, and a pivoting arm having electromagnetic transducers is used to read from, and write to, the disks. Both surfaces (upper and lower) of a disk can be used. This magnetic storage device is commonly referred to as a hard disk drive (HDD), and is usually packaged in a modular enclosure so that it may be easily installed in and removed from the computer system. Many computer systems use multiple HDDs for greater storage capability, or for fault tolerance, such as in a redundant array of inexpensive disks (RAID).
The magnetic disk of a typical HDD is divided into several different areas according to industry standards. For example, many disks include a master boot record for storing technical specifications of the disk, a boot sector for storing basic operating system data, and multiple tracks for storing other data. The transducers at the tip of the pivoting arm (rotary actuator assembly) must be precisely aligned with these various areas on the disk in order to properly write to or read from the disk. In the well-known Whitney style technology, the rotary movement and positioning of the actuator assembly is controlled by a series of electrical signals emanating from the computer processor (or from a "controller" connected to the processor), which feed into a voice coil motor (VCM) of the actuator assembly. The VCM includes an electromagnetic coil (solenoid) attached to a portion of the pivoting arm, and one or more permanent magnets are affixed to the HDD enclosure such that a steady-state magnetic field from the magnets can be used in conjunction with the magnetic field from the VCM coil to cause the arm to rotate about its pivot point in a precise manner. Many HDDs provide a special magnetic pattern, or "servo surface," that allows the actuator assembly to identify its relative location on the disk. In this manner, an actuator assembly can be quickly moved to the approximate desired location, and then precisely adjusted to the exact location.
One concern that arises with the foregoing construction relates to cooling of the VCM coil. During periods of extended use, the electrical signals passing through the wires heat the coil, which can lead to various problems. For example, a change in coil temperature affects the resistivity of the wire and therefore changes the electromagnetic response of the VCM. This variable response can lead to increased actuator move time since it is more likely to require additional fine tuning of the transducer location. Cooling of the VCM coil has therefore become increasingly important as greater demands are placed on input/output (I/O) performance. Also, power in the VCM coil increases inversely to the fourth power of the move time, so there are very large increases in coil power for small decreases (improvements) in actuator move time. Of course, excessive heating of the VCM coil can result in overheating of other sensitive (semiconductor) components of the HDD. The problem of VCM coil cooling is further exacerbated by the increasingly diminutive size of HDD enclosures.
One approach used to cool the VCM coil is to provide vents in the enclosure, to allow increased air circulation, but this introduces additional problems. In particular, when the HDD enclosure is not airtight, there is a risk that dust or other contaminants can be introduced into the enclosure. Dust particles on the disk surface can strike the transducer head and upset its flight, resulting in a "crash" of the HDD, and can lead to data loss. For this reason, vented enclosures must be provided with an air filter to trap particles before they can enter the drive. Microscopic contaminants, including corrosive pollutants, can still pass through the filter, however, so this approach is unsatisfactory when the computer system may be operating in a highly polluted environment. Also, vents allow introduction of water vapor into the enclosure which can be harmful to many components. Some HDDs provide a desiccant within the enclosure to battle water vapor, increasing the complexity (and cost) of the HDD. Finally, providing a vent alone does not ensure increased air circulation and some systems must additionally provide a fan or similar means for directing air flow to the HDD enclosure vent. Accordingly, most modern HDD enclosures do not use a vent, although they do provide "breather" filters which allow the pressure inside the enclosure to equilibrate with ambient pressure, such as where ambient pressure changes due to temperature or altitude. It would, therefore, be desirable to devise an improved method of cooling the VCM coil which does not require venting of the enclosure. It would be further advantageous if the construction were relatively inexpensive and easily adapted to existing HDD designs.